Brain estrogen receptors (ERs), like peripheral ERs, can be activated directly by estrogens, and presumably indirectly by ligand independent activation. The ligand independent pathway may mediate the effects of humoral factors and of afferent input derived from the environment on ER-containing neurons. The purpose of this Exploratory/Developmental grant application is to assess the usefulness of, and then further develop, a novel, transgenic, mouse strain, the ER action indicator (ERIN) strain of mice (which has a transgene, containing estrogen response elements on a promoter linked to a beta-galactosidase reporter gene) for studies of ligand independent activation of ERs in the brain. First the neuronal transgene response to estradiol will be characterized in populations of cells using an immunocytochemical technique, an essential first step. Then the usefulness of this mouse strain for studies of ligand-independent activation will be assessed. The long-range goal of this research is to understand the cellular processes by which afferent input from the environment, mediated by neurotransmitters and other humoral factors, act on neuronal ERs to modulate neuronal physiology and neuroendocrine events. In some experiments, ERIN mice crossed with strains of mice with ERalpha- or ERbeta-gene disruptions will be used to assess the role of each ER subtype in transgene responses to hormones, neurotransmitters, and second messenger pathways. This application is being submitted as an R21, because its purpose is to explore the use of a highly innovative approach (the ERIN mice) to a new area, the brain, and to develop this novel technology for additional work in this area, and to develop a body of data upon which significant future research may be built. This initial research is essential for future work on the molecular consequences of ligand independent activation of ERs in the brain of males and females, which can then be studied in an unprecedented way.